Efforts for research and development of batteries have been gradually materialized while the application of energy storage technologies is expanded to mobile phones, camcorders, notebook PCs, and electric vehicles, and electrochemical devices have received most attention in this respect.
Particularly, in line with the recent trends of electronic devices, efforts to develop lithium secondary batteries having small size and lightweight characteristics and capable of being charged and discharged to high capacity have continued.
A lithium secondary battery is composed of a positive electrode and a negative electrode, which include electrode active materials capable of intercalating/deintercalating lithium ions, a separator disposed therebetween, and an electrolyte as a lithium ion transfer medium.
The electrolyte currently used is a liquid electrolyte in which a lithium salt is dissolved in an organic solvent, wherein, since the electrolyte is at high risk of leakage, fire, and explosion and the growth of dendrites is possible, the electrolyte may cause self-discharge and heating of the lithium battery.
In order to improve the above disadvantages, various studies of a polymer electrolyte having a structure, in which a lithium salt is dissociated or impregnated in a polymer, instead of the liquid electrolyte, have recently been attempted.
Since the polymer electrolyte is not at risk of ignition in comparison to a case where the liquid electrolyte is used, it is known that the polymer electrolyte is suitable for a lithium secondary battery for an electric vehicle, or a large storage battery.
An electrolyte, which includes polyethylene oxide or polyether having ion dissociation ability in a main chain, has mainly been proposed as the polymer electrolyte. However, the polymer electrolyte has disadvantageous in that it has low ionic conductivity at room temperature and low temperature and has an oxidation stability of 4.0 V or less. Also, in a case in which the polymer electrolyte is composited with other conductive materials and used, it is disadvantageous in that lithium (Li) ion transfer numbers are different from each other to cause non-uniform ion transport on the surface of the electrode.
Thus, there emerges a need to develop a polymer electrolyte with a new configuration which may simultaneously improve mechanical properties and ionic conductivity while reducing interfacial resistance.